1. Field of the Invention
The present invention relates to telecommunication systems. In particular, the invention concerns a new type of method and system for registering an overload situation.
2. Description of the Prior Art
Open interfaces (V5.1 and V5.2) between an access network and a telephone exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards of the ETS 300 324 and ETS 300 347 series. V5 interfaces enable subscribers belonging to a physically separate access network to be connected to a telephone exchange using a standard interface. A dynamic concentrator interface V5.2 defined by the ETS 300 347-1 and 347-2 standards consists of one or more (1-16) PCM (Pulse Code Modulation) lines. One PCM line comprises 32 channels or time slots, each of which has a transfer rate of 64 kbit/s, so the total capacity of the PCM line 2048 kbit/s. The V5.2 interface supports analog telephones as used in the public telephone network, digital, such as ISDN (Integrated Services Digital Network) basic rate and primary rate interfaces as well as other analog or digital terminal equipment based on semi-fixed connections.
The maximum capacity of one V5.2 link is about 500 B-channels. This means that there may be about 500 calls going on at the same time. However, since the V5.2 interface is of a concentrating nature, this number of B-channels is sufficient to serve about 5000 subscribers, depending on the congestion level chosen by the operator. Subscribers may be connected to a local exchange e.g. via a special access node. The access node communicates with the local exchange e.g. via a V5 interface.
Subscribers can be connected to an access node via a wireless local loop system (WLL), in which case it is possible to concentrate subscribers at the interface between the access node and the wireless network. In practice, concentrating here means that not all the subscribers can be simultaneously connected to the access node, the capacity being only sufficient to serve a given number of subscribers.
In addition to actual signalling traffic, the V5 interface specifications include separate QandM interfaces (OandM, Operation and Maintenance) for a local exchange and an access network. A management interface Q3 for a local exchange is defined in ETSI standards ETS 300 379-1 and ETS 300 377-1. xe2x80x98Management interfacexe2x80x99 means an interface between a local exchange and a Telecommunications Management Network (TMN).
The V5 interface comprises two types of time slots: time slots reserved for speech communication, i.e. B-channels, and time slots reserved for signalling, i.e. C-channels. The V5.2 interface additionally comprises backup channels for the backup of the signalling channels. The backup channels normally carry no traffic. If a single 2-Mbit/s transmission link is used, the system automatically allocates time slot 16 for the control protocol. Time slots 16, 15 and 31 may be allocated for the public telephone network and ISDN channels. If there is more than one transmission link, then the system automatically allocates time slot 16 of the primary link for the control protocol, link control protocol, BCC (Bearer Channel Connection) protocol and backup protocol. Time slot 16 of the secondary transmission link is also reserved as a backup channel. The backup mechanism of the V5 interface ensures that a V5.2 interface containing many transmission links will work even after a malfunction has occurred in an individual PCM link. The backup mechanism is used to back up all active C-channels. The speech channels are not covered by the backup protocol. Time slots 1-31 can be reserved for the following purposes:
ISDN and PSTN (PSTN, Public Switched Telephone Network) B-channel,
communication channel carrying ISDM D-channel information, PSTN signalling or control data, or
communication channel carrying information pertaining to the Control-protocol, Link control protocol, Protection protocol or BCC protocol of the V5 interface.
The V5.2 interface specification includes the Control and PSTN protocols. Some of the functions of the Control protocol are e.g. to provide signalling channels in conjunction with call setup, control the states of subscriber ports and cooperate with the Protection protocol in a situation where a signalling channel connection is broken off. The Protection protocol protects the signalling channels e.g. in the event of a fault in the PCM line. one of the functions of the PSTN protocol is to transmit subscriber line status data to the access node in the case of an analog subscriber. The PSTN protocol additionally functions as a means of communicating with national PSTN specifications. The BCC protocol takes care of allocation and de-allocation of time slots in a concentrating interface. The protocols associated with the V5 interface are described in greater detail in ETSI standard series ETS 300 324 and ETS 300 347.
FIG. 1a presents a system comprising a V5.2 interface as defined in the ETS 300 347 standard series. The system presented in FIG. 1a comprises an access node AN and a local exchange LE. In this example, the access node is connected to the local exchange via a V5.2 interface which comprises links 6-9. The interface could also be V5.1, but in that case there is only one link, i.e. one PCM line between the access node and the local exchange.
The access node AN is provided with a management interface QAN and the local exchange is provided with a management interface QLE, allowing the local exchange and the access node to be controlled via the management interfaces QLE and QAN. The interfaces and structures of the management interfaces are defined in the standards mentioned above. The local exchange and the access node are connected to the management interface Q via the management interfaces QLE and QAN.
When a call is being set up from a local exchange to an access node or vice versa, the local exchange selects the V5.2 interface link to be used and a suitable time slot in that link. The BCC protocol according to the V5 standard gives the access node the link and time slot data so that the call can be set up. In a congestion situation, there may be no resource available for the call in the interface between the access node and the local exchange because of an overload in the interface, in which case the call cannot be set up. In practice, the calling subscriber does not get a dial tone be cause the subscriber cannot be even connected to the access node. This means that all speech time slots in the V5 interface are busy.
ETSI standard ETS 300 379-1, Annex B, comprises a definition to the effect that the indication of traffic measurements concerning the B-channels of the V5 interface is an allocation request between the resource manager and the BCC protocol object. The function of the resource manager is to be aware of which lines are free and which ones are busy. It determines which line is to be used for each call. The resource manager sends to the BCC protocol object an MDUTBCC (allocation request) message. As a response to this message, an MDU-BCC (allocation confirmation) primitive is sent.
However, problems are encountered in a situation where the resource manager finds that there are no resources available for a call and therefore makes no allocation request at all. In this case, there is no attempt to allocate a B-channel for the call, and therefore congestion due to a lack of resources is not recorded in the traffic measurement report. In other words, the above-mentioned standard does not require statistical information to be recorded about a situation where the resource manager of the local exchange detects an overload in the V5.2 interface. In such a case, the BCC protocol is not activated at all. According to the standard, the statistical recording system is only started when the allocation procedure. of the BCC protocol is started.
The present invention eliminates the drawbacks referred to above or at least significantly alleviates them. A specific aspect of the invention is to add a new property to the V5.2 interface by using a technique whereby the resource-manager""s information regarding an overload situation is utilized and a notice about the congestion situation is sent to a statistical unit.
The method of the invention concerns the registration of an overload situation in a telephone exchange system. The system of the invention comprises a local exchange, an access node and a concentrating interface, which may be a V5.2 interface and which connects the access node to the local exchange. The local exchange is preferably a DX200 manufactured by the assignee and the access node is preferably a DAXnode 5000.
In addition, the system comprises a resource manager, which is part of the local exchange, and a statistical unit, which is also part of the local exchange. In the method, the concentrating interface is scanned to find a free time slot therein. The resource manager detects that the concentrating interface is overloaded. This means that there are no free B-channels available for the setup of speech connections. According to the invention, based on information provided by the resource manager, a message reporting congestion is sent to the statistical unit. The message is preferably sent by the resource manager. The congestion situation is recorded in the traffic measurement report by the statistical unit.
The system of the invention sends a message reporting a congestion situation by means of the resource manager to the statistical unit and records a congestion situation in the traffic measurement report by means of the statistical unit.
In accordance with the invention, data indicating an overload situation where no more B-channels are available for allocation is recorded in the traffic measurement report.